In recent years, to eliminate the movable mura phenomenon in vertical alignment (VA) liquid crystal displays, the pixel unit of liquid crystal displays have adopted a charge-sharing technique to improve color shift at large viewing angle. Referring to FIG. 1, a charging gate 101, a sharing gate 102, and a common electrode line 103 and 104 are disposed on a first metal layer. A data line 105, a thin film transistor 106, and a sharing capacitor 107 are disposed on a second metal layer. Components of the first metal layer and components of the second metal layer are electrically connected to each other through contact holes 108 and 109. A pixel electrode layer disposed on the pixel array substrate fowls an opening, allowing light pass through. The opening is further partitioned into a main-opening 110 and a sub-opening 111. However, whether or not the charging gate line 101 and the sharing gate line 102 are being driven, a common electrode of a color filter substrate will cause a positive or negative bias on the sides of the charging gate line 101 and the sharing gate line 102, so as to rotate the liquid crystal and therefore forming light leakage regions 112, 113 and 114.
Referring to FIG. 2, under ideal conditions, the charging gate line 101, the sharing gate line 102, and the light leakage regions 112, 113, and 114 are disposed on the sides of the charging gate line 101 and sharing gate line 102, and are perfectly shielded by a black matrix 201 of the color filter substrate, therefore will not affect a black screen. However, in practice, a relative shift between the array substrate and the color filter substrate can easily occur because these two substrates are attached to each other by using adhesive at the edges of the panel in a vertical alignment liquid crystal display. As shown in FIG. 1, due to the presence of the sharing capacitor 107 and its metallic shielding effect, the light leakage region 114 below the sharing gate line 102 is apart from the sub-opening 111. On the other hand, the light leakage region 112 above the charging gate line 101 is close to the main-opening 110.
However, when an upward shift of the color filter substrate with respect to the array substrate occurs, a light leakage will not occur as long as the length of the shift is less than the width of the sharing capacitor 107, but when a downward shift takes place on the color filter substrate to the array substrate, even a small shift can cause light leakage. Referring to FIG. 3, a downward shift causes a white spot 301, which is due to light leaking through the light leakage region 112 when there is a black screen. Since the white spot 301 will occur when slapping the panel, it is known as movable mura. The solution of this phenomenon so far is to enhance the width of black matrix 201 of the color filter substrate. The black matrix 201 extends inward the main-opening 110 and an extending length is larger than the length of shifting length, so as to prevent light leakage from being exposed in the light leakage region, thus the movable mura is eliminated.
Yet the drawback of above-mentioned solution is that the panel aperture ratio decreases as the width of the black matrix 201 increases, thereby decreasing the transmission ratio of the panel. Accordingly, it is necessary to provide a pixel unit to solve the existing problem.